CareerCup-4.4

Given a binary search tree, design an algorithm which creates a linked list of all the 
nodes at each depth (i e , if you have a tree with depth D, you’ll have D linked lists) 

#include <iostream>  using namespace std;  typedef int Data;    struct Node  {      Node(Data d):data(d){left = right = NULL;};      Data data;      Node* left;      Node* right;  };struct ListNode{    ListNode(Node* n):data(n){next = NULL;};    ListNode* next;    Node* data;};  class Tree  {  public:      Tree():root(NULL){};      Node* root;      void insert(Data data, Node* node = NULL)      {          if(root == NULL)          {              root = new Node(data);              return;          }          if(node == NULL) node = root;          if(data == node->data)          {              return;          } else if(data < node->data) {              if(node->left == NULL)                  node->left = new Node(data);                  else                  insert(data, node->left);          } else {              if(node->right == NULL)                  node->right = new Node(data);              else                  insert(data, node->right);          }      };    int depth(Node* node)    {        if(node == NULL)            return 0;        int left = depth(node->left);        int right = depth(node->right);        return (left>right?left:right) + 1;    };    void createList()    {        int height = depth(root);        ListNode** ret = new ListNode*[height];        ret[0] = new ListNode(root);        for(int i=1; i<height; i++)        {            ret[i] = NULL;            ListNode* p = ret[i-1];            while(p != NULL)            {                if(p->data->left != NULL)                {                    ListNode* n = new ListNode(p->data->left);                    n->next = ret[i];                    ret[i] = n;                }                if(p->data->right != NULL)                {                    ListNode* n = new ListNode(p->data->right);                    n->next = ret[i];                    ret[i] = n;                }                p = p->next;            }        }        for(int i=0; i<height; i++)        {            ListNode* p = ret[i];            while(p != NULL)            {                cout<<p->data->data<<" ";                p = p->next;            }            cout<<endl;        }    }};    int main()  {      Tree tree;      tree.insert(5);      tree.insert(1);      tree.insert(7);      tree.insert(4);      tree.insert(3);    tree.createList();    system("pause");  };